Staff may have to repay unpaid tax if HMRC finds they incorrectly declared themselves as self-employed, rather than as employees.

The inquiries were revealed in a tax tribunal judgment involving newsreaders Tim Willcox and Joanna Gosling. They have appealed against a ruling by HMRC to pay extra tax and National Insurance contributions.

Jennifer Henderson, head of global mobility and employment tax at the BBC, told the tribunal that by autumn last year the number of inquiries into IR35 cases had risen to 100.

In a statement published on the BBC News website, the corporation said it was “up to individuals to ensure they pay the right tax”.

It read: “Since 2013, the BBC has adopted a new employment status test that provides a clear and consistent approach to the employment status of journalists and presenters.”

A HMRC spokeswoman said: “Employment status is never a matter of personal choice and is always dictated by the specific facts. When the employment relationship does not accurately reflect the underlying reality of the relationship, the wrong tax is paid then we intervene to ensure the rules apply as parliament intended.

“While there can be many legitimate business reasons for workers being employed through their own companies, there are rules in place enabling HMRC to make sure people who provide their services in this way pay the right tax and National Insurance.”